In this experiment you will use two different "slinky" springs to study and observe the various properties of wave motion. Waves can be made to travel down the length of the spring to reflect, to interfere, etc. The speed, frequency, and wavelength will be varied to see how they are related.
The fundamental properties of waves are related to each other. In fact, the relation is exactly the same for water waves, waves on a string, waves on a spring, sound waves, light, and all types of waves. The speed of the waves is the distance the wave travels per unit of time, v. The wavelength is the distance between two similar points on any two consecutive waves, say from crest to crest or trough to trough. This is usually represented by the Greek letter l . The frequency of the wave is the number of vibrations (or cycles) per unit of time. This is usually in the unit of cycles per second (or Hertz) and is designated by f. The relationship between these properties, which holds for all types of waves, is known as the wave equation.
Waves are classified as either transverse or longitudinal. In transverse waves, the particles of the medium move perpendicular to the direction that the wave moves. Longitudinal waves are those in which the particles of the medium move parallel to the wave direction. Water waves, however, are a combination of transverse and longitudinal waves. Standing waves can be set up by a repeated motion at one end of a spring at any one of several correct frequencies, where the length of the spring is some multiple of half the wavelength.
The spring can be held in the air by two people with the waves vibrating up and down and traveling along the spring from one end to the other. However, a better method consists of putting the spring on the floor, stretching it out a little and sending the pulses from side to side down the length of the spring. Please be very careful with these springs since they become easily tangled and are often ruined. Whenever you have them stretched, be very careful not to suddenly release one end! Also, when you finish with them, do not leave them tangled on your lab desk.
With these springs it is easier to observe transverse waves than longitudinal ones.
Next we will try some quantitative measurements.
Next, investigate the behavior of a single pulse down the short slinky stretched to the original length used for it in order to see how it reflects from the partners hand. This works better if the hand holding the end of the spring is "flipped" quickly to one side. Does it come back on the same side or the opposite side from the one on which it traveled toward your partner? Be sure you can tell which way. You may need to use a large amplitude pulse in order to see what happens better.
Next, you are going to set up standing waves in the long thin spring by using repeated motions at a constant rate.
Finally, the previous part of the experiment should also be performed by holding the spring in the air and vibrating one end of the spring up and down. Be careful not to let the end of the spring get away from you hand, since injury may occur.
Reflect upon the experimental observations that you have obtained today and comment on how the results compare with the book’s presentation of wave properties. In particular, what is it that the book tends to ignore that had a major impact on your observations?